CommonJS (Cjs)

Definition

• CommonJS is synchronous. Use in a Node.js environment
• By default, CommonJS file name is .cjs, or .js by default will be interpreted as CommonJS.
  • Note: unless you want to specifically state that the file only support CommonJS format, use .cjs since Node.js now also support ES6 format with version 13 and above with "type": "module" in package.json or just name the file .mjs
• CommonJS syntax can be used in browser with the support of RequireJS or BrowserifyJS

Syntax

Export

// src/index.js

class Logger {  
    log(content) {  
        console.log(content)  
    }  
}  
  
module.exports = new Logger()

Import

// index.js
var Logger = require('./src/logger.js')  
  
var data = [1, 2, 2, 3, 4, 5, 5, 5, 6];  
  
Logger.log(data);

Execution

Node.js

node index.js

Browser

To run CommonJS syntax in the browser, we can consider

• RequireJS: Support require() syntax in browser
• UMD: Support both browser and NodeJS
• BalbelJS: Bundle everything with a compilation before injecting inside browser
• SystemJS: Universal loader that support CommonJS (CJS), UMD and ECMAScript Module (ESM)